This invention relates to a compensator system with a compensator piston in the engine head with the purpose of the invention being first to provide a predetermined low compression ratio hereinafter referred to as a C.R. near the level commonly used for auto engines (near 9 to 1), and a very high C.R. near 15 to 1. The compensator system controls detonation with the engine operating at the high C.R. The C.R. can be changed from high to low for starting the engine in cold weather, and from low to high with the engine warmed up. A cooling system circulates water around the piston cylinder wall and circulates oil within the piston. A hydraulic return shock absorber slows the piston return speed to prevent noise and vibrations as the piston is returned to rest position.
The engine can be operated with low octane gasoline, methanol, or ethanol fuels.